Altered expression of antimicrobial peptide genes in the skin of dogs with atopic dermatitis and other inflammatory skin conditions

Background: Reports indicate that human and canine patients with atopic dermatitis (AD) have reduced production of several skin antimicrobial peptides, but more recent data have called those results into question. Hypothesis/Objectives: To compare the mRNA expression of seven antimicrobial peptide genes in lesional and adjacent nonlesional skin biopsy specimens from dogs with AD with those from normal dogs and from dogs experiencing other inflammatory skin conditions. Animals: Normal dogs and patients with AD or other inflammatory skin conditions were enrolled with owner permission and approval of the Institutional Animal Care and Use Committee. Methods: Transcripts were measured by quantitative RT-PCR using a standard curve assessment. Results: Normal transcript levels for all seven antimicrobial peptides varied depending on the body site assessed. Transcripts for secretory leukocyte proteinase inhibitor (SLPI) and skin-derived antileucoproteinase (SKALP; also known as elafin) were typically ~10-fold greater in number than transcripts for the canine β-defensins (CBD)-1, -102, -103, -122 and -124. Transcripts for SKALP, SLPI, CBD-1, CBD-103 and CBD-122 were lower in both lesional and adjacent nonlesional skin from dogs with AD in comparison to normal skin. Transcripts were reduced to a similar extent versus normal dogs in skin of dogs with inflammatory skin conditions from both lesional and nonlesional biopsies, except for CBD-122, which was reduced only in lesional skin. Compared with normal dog skin, transcripts for CBD-102 and CBD-124 were unaffected in dogs with AD. Conclusions and clinical importance: Both SKALP and SLPI may be important contributors to skin innate immunity, but their decreased expression in AD patients does not account for increased skin infections compared with other skin conditions.